Firefles in Glass rendering
What helped me most times is increasing the size of the light source. At default, e.g. point lamps have a size of 0.1 units, so when calculating caustics blender just has rounding errors, I guess.

Of course, raising the size of your light source higher and higher will produce softer and softer shadows, so you have to play with the values.

Another guess: Don't lighten your scene with objects with emission materials alone – they will not produce enough light. Add standard point or area lights where necessary.